Caries is defined as the progressive decay of tooth or bone, and dental caries is the most common ailment known world wide. Dental caries can be treated by either removing the decayed material in the tooth and filling the resultant space with a dental amalgam, or in severe cases, by removal of the entire tooth.
The early diagnosis of dental caries is of utmost importance to any subsequent treatment since by the time pain is felt due to decay of the tooth, the treatment required to restore the tooth may be extensive and in some cases, the tooth may be lost.
Historically, the diagnosis of dental caries has been primarily visual, frequently accompanied by tactile examination using a mechanical probe. The patient may only seek an examination by a dental surgeon when in pain due to the caries and the surgeon must then identify the offending tooth by visual examination and/or by use of a mechanical probe which causes discomfort or pain in the decayed tooth. This experience is painful and distressing for the patient and acts as a disincentive to regular visits to the surgeon for routine examinations. In addition, the diagnosis of caries at this late stage of decay reduces the available options for treatment.
The diagnosis of caries by conventional techniques has become increasingly difficult. This is a result of several factors, including apparent changes in the morphology and in the rate of progress and distribution of carious lesions, as well as the inaccessibility of approximal (mutually contacting) dental surfaces and the complicated anatomy of pit and fissure sites on the occlusal (biting) surfaces.
An additional problem with conventional techniques is that decay on the approximal surface of the tooth resulting from plaque on the inter dental spaces may not be detected by simply prodding the tooth, since the approximal surfaces may not be reached by the probe. The limitations of conventional visual, tactile and radiographic diagnosis are well recognised. Decay may progress to an advanced stage on both occlusal and approximal sites without being detected until substantial tooth destruction has occurred.
In response to these generally unsatisfactory and unreliable methods of diagnosis attempts have been made to develop electrical/electronic means for the diagnosis of caries.
Electronic Caries Detectors (ECD's) generally comprise a probe having a first, probe electrode which is placed in contact with the tooth to be tested, and a second, counter electrode separate from the probe which is placed in contact with another part of the body of the patient in order to complete an electrical circuit connecting the two electrodes. The second electrode may be held by the patient or may be placed in contact against the gingiva (gum) or oral mucosa (inside cheek). An alternating electric current of fixed frequency is passed through the tooth and the resistance to this is measured. This electrical resistance has been found to correlate approximately inversely with the extent of caries in the tooth. The technique may involve measurement at a single point on the surface of the tooth, or the use of an electrically conductive paste, providing a measurement for the surface as a whole.
The configuration of conventional designs of ECD probes are such that they cannot contact approximal tooth surfaces, and therefore cannot detect approximal caries which does not extend to the occlusal or free smooth surfaces of the tooth. No satisfactory means to detect such approximal caries is currently known, although the problem of approximal caries has been prevalent for many years. Hitherto, the most accurate method of diagnosing approximal caries has been bitewing radiography, but this method is only about 30% accurate and requires the use of ionising radiation.
Even where good electrical contact can be established between the probe electrode and the relevant site, conventional ECD apparatus is of limited usefulness in the detection of caries.